1. Field of the Invention
The invention relates to a doctor device for metering and/or leveling a liquid to pasty medium applied to a moving surface, the surface in the case of direct application of the medium being a paper, board or other fibrous web and in the case of indirect application being the surface of a transfer element which transfers the medium to the fibrous web.
2. Description of the Related Art
During the application, the application layer is normally applied in excess and therefore has to be doctored off to the desired coating weight, that is to say metered. On the other hand, if the application medium is applied exactly in the desired coating quantity, it merely has to be leveled or evened out by the doctor device, that is to say by a doctor element fitted in the doctor device.
EP-B1 0 682 728 discloses a metering unit or doctor device. It has a holding part for holding a rotatable, cylindrical metering rod.
In addition, in the interior of the holding part there is arranged a pressure tube or a large number of individual tubes lined up in a row with one another, with the aid of which the metering rod is pressed against the surface to be treated. The installation and removal of the tube or also of a large number of tubes, as well as the cleaning of the device, are complicated and relatively lengthy.
In other known doctor devices (e.g. DE-A1 295 10 486, DE-A1 196 19 249), a clamping tube required in order to fix the doctor device is arranged in a fixed manner in or on a holder or a supporting element.
In some designs, the clamping tube is subjected to a high level of contamination. In addition, the clamping tube makes cleaning more difficult overall and also of the holder, for which reason relatively long stoppages of a coating machine occur during cleaning work. As a result of contaminants in the doctor holder, a nonuniform transverse profile arises in the coating medium applied. The nonuniform transverse profile leads to unplanned stoppages. In addition, during the cleaning work it is possible for the maintenance personnel to destroy the clamping tube and also a pressure tube which is present, because of the poor accessibility of the contaminants.
What is needed in the art is an improved doctor device which can be constructed and mounted more simply than hitherto and whose cleaning is more simply possible.